Water 2015, 7, 1538-1567; doi:10.3390/w7041538 OPEN ACCESS water ISSN 2073-4441 www.mdpi.com/journal/water Article Combined Impacts of Medium Term Socio-Economic Changes and Climate Change on Water Resources in a Managed Mediterranean Catchment Anastassi Stefanova *, Cornelia Hesse and Valentina Krysanova Potsdam-Institute for Climate Impact Research, Post Box 601203, Potsdam 14412, Germany; E-Mails: [email protected] (C.H.); [email protected] (V.K.) * Author to whom correspondence should be addressed; E-Mail: [email protected]; Tel.: +49-331-288-2461. Academic Editors: Lutz Breuer and Philipp Kraft Received: 2 February 2015 / Accepted: 27 March 2015 / Published: 10 April 2015 Abstract: Climate projections agree on a dryer and warmer future for the Mediterranean. Consequently, the region is likely to face serious problems regarding water availability and quality in the future. We investigated potential climate change impacts, alone (for three scenario periods) and in combination with four socio-economic scenarios (for the near future) on water resources in a Mediterranean catchment, whose economy relies on irrigated agriculture and tourism. For that, the Soil and Water Integrated Model (SWIM) was applied to the drainage area of the Mar Menor coastal lagoon, using a set of 15 climate scenarios and different land use maps and management settings. We assessed the long-term average seasonal and annual changes in generated runoff, groundwater recharge and actual evapotranspiration in the catchment, as well as on water inflow and nutrients input to the lagoon. The projected average annual changes in precipitation are small for the first scenario period, and so are the simulated impacts on all investigated components, on average. The negative trend of potential climate change impacts on water resources (i.e., decrease in all analyzed components) becomes pronounced in the second and third scenario periods. The applied socio-economic scenarios intensify, reduce or even reverse the climate-induced impacts, depending on the assumed land use and management changes. Water 2015, 7 1539 Keywords: Mar Menor; socio-economic changes; land use change; management change; climate change impacts; eco-hydrological modelling; Soil and Water Integrated Model (SWIM) 1. Introduction The climate of the Mediterranean region is especially vulnerable to potential changes in the global circulation processes [1]. It is therefore not surprisingly, that Giorgi [2] identified the region of the Mediterranean as a primary climate change “Hot-Spot” based on projections of Phase 3 of the Coupled Model Intercomparison Project (CMIP3) for the late 21st century. More recently, Diffenbaugh and Giorgi [3] confirmed this result using a similar but more comprehensive approach and an ensemble of CMIP5 Representative Concentration Pathway (RCP) 8.5 and RCP4.5 simulations. The agreement among climate models for the Mediterranean region is considerably strong compared to other regions in the world [4] and so are the trends for temperature and precipitation changes. Several studies state that the Mediterranean region is very likely to become dryer and warmer in future, as global warming continues (e.g., [5–9]). In consequence, the area is expected to face serious problems, such as agricultural production losses, land degradation and habitat losses [10]. Moreover, a decrease in water availability will in addition enhance the competition for water between economic sectors and by that the vulnerability of the Mediterranean countries to changes in climate [11]. Our study area, the catchment of the Mar Menor, a hyper saline lagoon in southeast Spain, is one of the driest and hottest regions in Spain and on the Iberian Peninsula [12]. The region is exposed to a severe water stress under the current climate [13] and still, due to intensive irrigation, is one of Europe’s major horticultural producers and exporters [14,15]. Apart from agriculture, mass tourism along the shoreline of the lagoon is also highly important for the local economy. The rapid development of both sectors during the last decades was possible due to the Tagus-Segura Inter Basin Transfer (IBT) that has been delivering water from the Tagus River to the Mar Menor catchment since 1978 [16]. Since then, the major watercourse in the catchment, the Albujon wadi, inputs regularly and especially during the wet period high amounts of nutrients from the adjustment agricultural fields to the lagoon [17]. Moreover, insufficiently treated effluents coming mainly from the touristic areas and reaching a maximum during the touristic peak in summer have been discharged into the same wadi over a long period [18]. These inputs have resulted in a rapid increase of the pollution in the lagoon [19–22], and need to be addressed urgently in order to prevent the ecosystem from further degradation. In addition to current anthropogenic pressures, climate change is expected to pose further stress to the Mar Menor and its drainage area. An increase in sea water temperature, for example, is very likely to lead to an intensification of the eutrophication processes in the lagoon, and finally to a collapse of the water body [23]. Climate change will also affect the water resources in the donor basin of the IBT, the Tagus River Basin. According to Killsby et al. [23] the discharge of the Tagus River is likely to get reduced by almost a half (49%) until the end of the century, due to climate change. Consequently, the water resources transferred to the Mar Menor catchment could also decrease, which will certainly affect the agricultural and touristic sectors, and by that also the water and nutrient inputs to the lagoon. The Water 2015, 7 1540 natural, non-managed water resources in the catchment will be affected by climate change too and will most probably further decline, as climate becomes dryer. CMIP3 model simulations for the Mediterranean region project a long-term decrease in precipitation of about 15% for the end of the century (2070–2099) and of 8% for the near future (2020–2049) compared to 1950–2000 [24]. Based on their results, Mariotti et al. [24] expect a decrease in runoff and river discharge as well, which would certainly reduce the water available for irrigation and other uses, as climate change continues. A study on the impacts of climate change on water resources in Spain in particular [25] identified the Segura region, in which the catchment of the Albujon wadi is located, as highly critical regarding the hydrological implications of future climate. More recently Mariotti et al. [26] investigated the long-term climate changes in the Mediterranean region using the newly available CMIP5 model simulations, and obtained similar results as in their previous study. The arid and semi-arid regions in the Mediterranean are projected to become dryer, especially during the wet season (December–February), whereas there is no significant decrease in precipitation projected for the already dry summer (June–August) season [26]. Another study comparing the A1B emission scenario (balanced emphasis on all energy sources) simulations of CMIP3 with the RCP4.5 and 8.5 simulations of CMIP5 for the Mediterranean region on the seasonal basis [27] also identified a consistency between both types of scenarios. This indicates a robustness of future climate trends simulated for the region [27], and thus a warmer and dryer future for the Mar Menor catchment becomes even more plausible. We therefore decided to assess the response of the Mar Menor catchment to potential changes in climate because of its importance for the ecological status of the lagoon and the region’s economy. Moreover, as the water resources in the catchment are strongly human influenced, the vulnerability to climate change was studied in combination with potential changes in land use and water management. For that, we firstly quantified the total amount of water and nutrient inputs to the Mar Menor using the eco-hydrological Soil and Water Integrated Model (SWIM, [28]). The model was then driven by a set of 15 regional climate scenarios from the ENSEMBLES project [29] for one reference and three future scenario periods, of 30 years each. Next, four different socio-economic scenarios, including new land use maps and water management settings were run in combination with the 15 climate scenarios for the near future scenario period. The results of this study were used for further analysis. They were used as input data to a specific lagoon model that can investigate the lagoons response to changes in its drainage basin, and also as scientifically founded information for stakeholders and policy makers and their future planning and decisions. 2. Case Study Area Description The catchment of the Mar Menor is situated on the Mediterranean coast in southeast Spain, in the region of Murcia. It covers an area of about 1380 km2 and overlaps almost entirely with the basin of the Campo de Cartagena aquifer (Figure 1). The Albujon wadi is the major watercourse in the catchment and drains, together with several smaller, so called ramblas (ephemeral water courses with uncontinuous flow), into the Mar Menor. However, there are no gauging stations in the catchment, not even on the Albujon wadi. The main soils are deep Cambisols with low permeability (76%), and agricultural land occupies about 82% of the area. Water 2015, 7 1541 Figure 1. Geographical location of the Mar Menor catchment and major characteristics of the case study area. The drainage area has a gentle slope and elevations ranging from 1062 m.a.s.l at the low mountainous range Sierra de Carrascoy in the West to −5 m.a.s.l. at the Mediterranean coast in the East. The climate is semi-arid Mediterranean, characterized by dry and hot summers and mild winters. The mean annual temperature is about 18 °C, and the mean annual precipitation about 300 mm, mostly occurring during short episodic storm events in autumn and spring.